The present invention relates to a color image forming apparatus or system wherein, after a colored document has been read by a reading section, the image data constituting a color image is stored into image storing devices separately for each color, particularly to the art of performing the functions of a color image forming apparatus or system even if some of the image storing device have been damaged.
A color image forming apparatus such as a copying machine is normally designed to achieve full-color image formation using the four colors of yellow (Y), magenta (M), cyan (C) and black (K). These four colors are managed as the image data for each color in the apparatus. A large capacity storage apparatus such as a magnetic disk device is commonly used as the image storing device for temporarily storing the image data in the apparatus. Four image storing devices for the respective colors are provided to implement high-speed input and output operations. They are operated in parallel for simultaneous four-color processing. This structure increases the processing speed virtually 400 percent, as compared to the case where image data for each color is stored sequentially into one image storing device.
Such a color image forming apparatus is equipped with multiple image storing devices. Accordingly, problems can occur that much sooner and, if any one of the devices has broken, the apparatus cannot function as a color image forming apparatus.
Various techniques have been proposed in an effort to ensure that the apparatus as a whole will operate correctly even if there are problems in some of the image storing devices. One of these proposals relates to an apparatus equipped with magnetic disk devices. Such a device having a drive mechanism as a magnetic disk device is more likely to have problems. An image forming apparatus is proposed in the Official Gazette of Japanese Patent Tokkai 2000-215008, wherein this image forming apparatus is provided with a recovery means for changing the storage site of the program data or the storage site of the image data so that the apparatus can be operated by the other normal magnetic disk devices if any one of them has broken down.
Another proposal is published in the Official Gazette of Japanese Patent Tokkaihei 10-32690, wherein, if one of the image storing devices for storing the image data for each color is fully loaded, the image data of the color allocated for the fully loaded image storing device is loaded into another image storing device so that the operations of the apparatus can be performed.
If the image data of the color allocated for the image storing device with a problem is stored in another normally operative image storing device that is free from any problem, the image storing device with the added load will take a longer time to store the image data than otherwise. However, the document reading time and image formation processing speed in the color image forming apparatus are set based on the storage time and reading time when all the image storing devices are normally operating. Accordingly, the image storing device with an added load cannot meet the time requirements for storage and reading of the image data. If there are not many pages, the shortage of processing time can be covered by a buffer memory. However, when many pages must be processed continuously, the shortage of processing time cannot be covered by the buffer memory alone. As a result, the document reading operation or image formation operation is suspended. This has created a problem in prior art.